And it makes rotation of a few unrotated files in a big folder to be very slow!

I got a folder with images from a camera. Some of them have exif information about rotation and I want to rotate them.
When I select all of the images in the folder and then command XnView to rotate them by exif tag, this takes a lot of time, even if there are only few images to be rotated.

I see in Total Commander that when rotating there are creation of temporary "JP_" files for every image in the folder! But it seems to be reasonable to backup only images to be rotated.

For example, I have after photosession a folder with 100 images only 10 of them were shot with vertical camera orientation.

1) I select in XnView all of the files in the photosession folder. (This is reasonable, because to select one-by-one only 10 "vertical" images is uncomfortable and time consuming.)

2) Then I command to rotate these jpgs by exif tag information.

3) XnView creates bkups for every file of this 100 files, but 90 files are needless to rotate (so needless to backup!) This is very time consuming, especially for usb flash.

In the above example, FastStone Image Viewer process only images to be processed. Given for example folder of images with none to exif-rotate, FastStone Image Viewer says that there's nothing to rotate, but XnView starts to process every file with creation of unnecessary bkups.